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B. Cense, W. Gao, O. P. Kocaoglu, Q. Wang, D. T. Miller; Henle’s Fiber Layer Birefringence Measurements With PS-OCT. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6367.
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The structured organization of Henle’s fiber layer causes birefringence, a difference in refractive index in which light polarized perpendicular and parallel to the fiber are differentially retarded. Macular diseases such as age-related macular degeneration and diabetic retinopathy are known to disrupt the organization of the fibers and a change in birefringence may therefore be an early indicator of retinal disease. Birefringence of Henle’s fiber layer has been reported using a variety of techniques, including polarization-sensitive optical coherence tomography (PS-OCT), a technique that provides depth-resolved phase retardation and intensity images of the retina. While PS-OCT has provided qualitative assessment of birefringence of this layer, the 3D distribution of the birefringence has not been quantified.
We used a PS-OCT system that records intensity and depth resolved birefringence simultaneously. By modulating the input polarization state, the retinal measurements taken with this PS-OCT system are insensitive to birefringence of cornea and lens. The input power into the eye was 600 µW, well below the ANSI limit. The right eyes of five healthy subjects were imaged with PS-OCT without dilation in sessions of 5 to 10 minutes. A fixation target for the subject was used to center all measurements at an eccentricity of 0°. Stationary horizontal and vertical scans with a width of 20° (~ 6mm) and volumes of 20° x 20° were recorded at an A-line acquisition rate of 25kHz.
An example of a paired intensity and double pass phase retardation (DPPR) image is given in Figure 1. For the five eyes, preliminary results indicate that Henle’s fiber layer generates a measureable DPPR of approximately 17º from 1.0º ± 0.2º retinal eccentricity to 5.1º ± 1.3º.
PS-OCT is sufficiently sensitive to quantify the distribution of birefringence in Henle’s fiber layer in healthy subjects.
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